Physical model of near-Earth asteroid (1917) Cuyo from ground-based optical and thermal-IR observations

Context: The near-Earth asteroid (1917) Cuyo was subject to radar and lightcurve observations during a close approach in 1989, and observed up until 2008. It was selected as one of our ESO Large Programme targets, aimed at observational detections of the YORP effect through long-term lightcurve monitoring and physical modelling of near-Earth asteroids. Aims: We aimed to constrain physical properties of Cuyo: shape, spin-state, and spectroscopic & thermophysical properties of the surface. Methods: We acquired photometric lightcurves of Cuyo spanning the period between 2010 and 2013, which we combined with published lightcurves from 1989-2008. Our thermal-infrared observations were obtained in 2011. Rotationally-resolved optical spectroscopy data were acquired in 2011 and combined with all available published spectra to investigate any surface material variegation. Results: We developed a convex lightcurve-inversion shape of Cuyo that suggests the presence of an equatorial ridge, typical for an evolved system close to shedding mass due to fast rotation. We determine limits of YORP strength through lightcurve-based spin-state modelling, including both negative and positive acceleration values, between -0.7x10-8 rad day-2 and 1.7x10-8 rad day-2. Thermo-physical modelling with the ATPM provides constraints on the geometric albedo, PV = 0.24 ± 0.07, the effective diameter Deff = 3.15 ± 0.08 km, the thermal inertia, 44 ±- 9 J m-2s-1/2K-1, and a roughness fraction of 0.52 ± 0.26. This enabled a YORP strength prediction of (-6.39 ± 0.96)x10-10 rad day-2. We also see evidence of surface compositional variation. Conclusions: The low value of YORP predicted by means of thermophysical analysis, consistent with the results of the lightcurve study, might be due to the self-limiting properties of rotational YORP, possibly involving movement of sub-surface and surface material. This may also be consistent with the surface compositional variation that we see. The physical model of Cuyo can be used to investigate cohesive forces as a way to explain why some targets survive rotation rates faster than the fission limit

On the origin and evolution of the material in 67P/Churyumov-Gerasimenko

International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects

Repeat Instability in the 27-39 CAG Range of the HD Gene in the Venezuelan Kindreds: Counseling Implications

The instability of the CAG repeat size of the HD gene when transmitted intergenerationally has critical implications for genetic counseling practices. In particular, CAG repeats between 27 and 35 have been the subject of debate based on small samples. To address this issue, we analyzed allelic instability in the Venezuelan HD kindreds, the largest and most informative families ascertained for HD. We identified 647 transmissions. Our results indicate that repeats in the 27-35 CAG range are highly stable. Out of 69 transmitted alleles in this range, none expand into any penetrant ranges. Contrastingly, 14% of alleles transmitted from the incompletely penetrant range (36-39 CAGs) expand into the completely penetrant range, characterized by alleles with 40 or more CAG repeats. At least 12 of the 534 transmissions from the completely penetrant range contract into the incompletely penetrant range of 36-39 CAG repeats. In these kindreds, none of the individuals with 27-39 CAGs were symptomatic, even though they ranged in age from 11 to 82 years. We expect these findings to be helpful in updating genetic counseling practices. © 2008 Wiley-Liss, Inc.link_to_subscribed_fulltex